A number of various extracorporeal blood treatments exist. Examples are hemodialysis, hemofiltration and hemodiafiltration, which all make use of a filter and are often called dialysis. Dialysis may also be performed as peritoneal dialysis, where no withdrawal of the blood takes place. Instead a so called pd-solution is kept in the abdominal cavity of the patient for specified periods of time.
A conventional filter for dialysis comprises a first and a second compartment separated by a membrane. The first compartment has an inlet and an outlet for the circulation of blood there through. The second compartment has an outlet for draining a liquid (e.g. plasma water and used dialysis liquid) and in case the treatment (as in the case of hemodialysis) requires the circulation of a treatment liquid (e.g. a dialysis liquid), the second compartment also has an inlet.
In the above treatments, blood is withdrawn from the patient, flown through the first compartment of the filter, and returned to the patient. This part is the so called extracorporeal blood circuit. In case excess water is to be withdrawn from the blood, this is done across the membrane. In hemodialysis, a dialysis liquid is simultaneously flown through the second compartment of the filter and the metabolic wastes contained in the blood migrate by diffusion over the membrane into the second compartment. In hemofiltration, a pressure difference is created across the membrane so that plasma water flows through the membrane into the second compartment. Metabolic wastes migrate by convection into the second compartment. In order to compensate for the excess loss of body fluid, the patient is simultaneously infused with a sterile substitution solution. Hemodiafiltration is a combination of hemodialysis and hemofiltration. In this treatment a dialysis liquid is flown through the second compartment and a substitution solution is infused into the patient.
The dialysis liquid is thus flown from a fluid source and into a fluid circuit, which comprises the second compartment of the filter, where the blood is treated. After having passed the second compartment of the filter, the dialysis liquid is disposed to a drain.
There are a number of ways to prepare the dialysis fluid and the replacement fluid, both called treatment fluid below. Basically, different components, often in the form of a concentrate in fluid or powder form, are to be mixed with pure water. Generally the preparation can be done according to one of two basic principles. The first one is batch preparation and the second one is on-line preparation. In batch preparation the treatment fluid is prepared before the treatment starts. All components that are needed are put into a container together with water and a mixing takes place. Thus, the concentration of the different components in relation to each other cannot be changed once the treatment has started. This document will focus on the on-line preparation.
In on-line preparation of a treatment fluid, the preparation is continuous during the session of blood treatment of a patient. The preparation typically includes feeding of water in a main line and adding the concentrates one after the other along the main line. A ready-to-use treatment fluid is delivered at the downstream end of the main line. Thus, the downstream end of the main line is the output from the fluid source mentioned above. Thus, in the case of a dialysis liquid, the downstream end of the main line is directly connectable to the upstream end of the fluid circuit. As is known in the art, the fluid source is typically part of a dialysis machine. The concentrates that are being added to the main line are typically in fluid or powder form and are being fed by one pump each. If two concentrates are needed for the dialysis liquid, one may be in fluid form and the other one may be in powder form.
If the concentrate is in fluid form, it is fed by a pump in a feeding line, which is connected to the main line at a mixing point. The concentrate is fed at a suitable feeding speed to be properly diluted when it is mixed with the water in the main line.
If the concentrate is in powder form, the continuous preparation typically includes feeding a stream of water into a container that holds a concentrate in powder form that is dissolved by the water. The water and the dissolved substance form a fluid concentrate, which is delivered from the container and which is treated in the same way as the fluid concentrate above.
Typically, more than one concentrate have to be diluted with water and mixed together to achieve a treatment fluid with all required components, each concentrate having its own pump.